September 2, 1892.] 



SCIENCE. 



139 



tioDS of the ratio O : H. For many of the problems, however, 

 the atomic weights are rounded to whole numbers, except CI = 

 35.5. 



The work is recommended as a well-planned text-book of the 

 subjects indicated. 



Mechanics for Beginners. Part I. Dynamics and Statics. By 

 J. B. Lock. London and New York, Macmillan & Co., 

 1891. 



Thls is a carefully-prepared elementary textbook, jiresenting 

 the subject in the following order: rectilinear motion, motion in 

 one plane, forces acting at a point, parallel forces, machines 

 (including friction), uniform motion in a circle, energy, the pen- 

 dulum. The definitions are clear and examples abundant. The 

 demonstrations presuppose a knowledge of trigonometry. 



English units are employed throughout. The following terms 

 are convenient (in the absence of metric units), but not very 

 familiar in this country : velo, the velocity of one foot per second; 

 celo, the acceleration of one velo per second; poundal, a force pro- 

 ducing one celo on one pound; and foot-poundal, the work done 

 by one poundal acting one foot. 



While this work shows marks of thoroughness, it seems a 

 great pity to ignore the international system of weights and 

 measures. 



Elementary Lessons in Heat. By S. E. Tillman Revised Edition. 



New York, John Wiley & Sons, 1893. 



These lessons, prepared as a short course for the U. S. Military 



Academy, present the most essential and practical aspects of the 



subject, in a clear and descriptive manner. The language of 



trigonometry and differential calculus are scarcely introduced, 

 even in discussing the conduction of heat. English units are em- 

 ployed, for the most part. The various kinds of thermometers 

 and other instruments required by observers are explained ; and 

 the last two chapters are devoted to meteorology. 



Forty -six numerical problems are added in this edition, illus- 

 trating thermometric scales, linear and cubic expansion, properties 

 of gases, specific heat, latent heat, relative humidity, and me- 

 chanical equivalent of heat. 



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